Pharmaceuticals intended for oral administration arc typically provided in solid form as tablets, capsules, pills, lozenges, or granules. Tablets are swallowed whole, chewed in the mouth, or dissolved in the oral cavity. Soft tablets that either arc chewed or dissolve in the mouth are often employed in the administration of pharmaceuticals where it is impractical to provide a tablet for swallowing whole. With chewable tablets, the act of chewing helps to break Up the tablet particles as the tablet disintegrates and may increase the rate of absorption by the digestive tract. Soft tablets are also advantageous where it is desirable to make an active ingredient available topically in the mouth or throat for both local effects or systemic absorption. Soft tablets are also utilized to improve drug administration in pediatric and geriatric patients. Soft tablets designed to disintegrate in the mouth prior to swallowing are particularly useful for improving compliance of pediatric patients.
Generally, soft tablets are made by compaction of a mixture of tabulating compounds including an active ingredient, flavoring, binders, etc. The mixture is fed into a die cavity of a tablet press and a tablet is formed by applying pressure. Hardness of the resulting tablet is a direct function of the compaction pressure employed and the compatibility oi the ingredients in the formulation. A softer tablet, having an easier bite-through, may be prepared by employing reduced compaction pressures. The resulting tablet is softer, but also more fragile, brittle, and easily chipped.
Soft tablets designed to disintegrate in the mouth without chewing are disclosed by Cousin et al., in U.S. Pat. No. 5,464,632, and Wehling et al., in U.S. Pat. Nos. 5,223,264 and 5,178,878. While these soft tablets for oral administration advantageously disintegrate completely in the mouth prior to swallowing, they have the disadvantage of being highly friable, requiring costly specialized handling and packaging in order to prevent breakage.
Several workers in the field have described chewable tablets comprising an active ingredient and a fatty or polymeric binder material. PCT Application No. WO 93/13758 describes tablets made by combining and compressing a meltable binder, excipients, and a pharmaceutically active ingredient into a tablet, melting the binder in the tablet, and the solidifying the binder. During the melting step, the binder, a material such as a natural fat or polyethylene glycol, flows and fills in minor cracks within the tablet. If a coating is desired on the tablet, it must be coated with a coating material in a separate step.
U.S. Pat. No. 4,684,534 discloses a chewable tablet having a harder outer shell and a softer interior. The tablet is made from agglomerates comprising a carbohydrate and a small amount of a carbohydrate binder such as maltodextrin, in addition to the active ingredient. The agglomerates are compressed into a tablet, resulting in the harder outer shell surrounding the softer interior. The hardness of the outer shell is on the order of 6 to 18 kp.
It has now been discovered that a tablet, preferably a soft tablet, having a core/shcll configuration may be made from a mixture comprising at least one active ingredient and a binder having a melting point of about 20 to about 180.degree. C. A granular agglomerate is formed from the mixture, and heated to melt the binder only at or near the surface of the granular agglomerate. The granular agglomerate is then cooled such that the melted binder solidifies into the continuous phase of a fused layer, which surrounds and protects the core of the tablet.